Vibe-coded MVP worked great, then real users broke the admin dashboard

Spent the last few weeks building three connected apps and shared microservices with Lovable/Cursor. The first 80% went shockingly smooth, the demo-stage stuff always does. Then real usage started, and the integration between services and the admin dashboard started throwing constant sync errors. A few different AI coding tools could patch individual symptoms but never quite nail the root cause.

For anyone who's taken an AI-built app past the demo stage: what was the first thing that actually broke once real users or data hit it, auth, data consistency, service integration, something else? And did you end up digging into the code yourself, or bring in outside help to sort it out?